The discovery that some platinum complexes are active against tumors has brought about a renewed interest in metal complexes as a source for anti-cancer agents. Cisplatin, cis-[Pt(NH.sub.3).sub.2 Cl.sub.2 ], for example, has been singularly successful in bringing about a regression of testicular and ovarian tumors and, as a result, other platinum derivatives have been investigated for anti-tumor activity. This led to the extensive testing of platinum and other transition metal compounds for anti-tumor activity in animals (Cleare; "Coordination Chemistry Reviews"; 12: 349 (1974); and Connors and Roberts, ed., "Platinum Coordination Complexes in Cancer Chemotherapy", Springer; New York (1974)). The neutral complexes: cis-[PtA.sub.2 X.sub.2 ] have been shown to be most active against animal tumors but, as a class, they are not very soluble in water (J. L. Marx; "Science", 192: 774 (1976)). Cleare and Hoeschele indicate solubilities in water or saline which range from 0.04 g/100 ml for [Pt(CH.sub.3 NH.sub.2).sub.2 (malonate)] to 1.38 g/100 ml for [Pt(CH.sub.3 NH.sub.2).sub.2 Cl.sub.2 ] at 37.degree. (Cleare and Hoeschele, "Bioinorganic Chemistry"; 2: 187 (1973)). Unfortunately, such low solubilities render them less desirable for oral or intravenous administration.